usb: gadget: udc: pxa27x: do not rely on 'driver' argument

future patches will remove the extra 'driver'
argument to ->udc_stop(), in order to do that,
we must make sure that our UDC does not rely
on it first.

Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/udc/pxa27x_udc.c

@@ -1862,7 +1862,7 @@ static int pxa27x_udc_stop(struct usb_gadget *g,
 {
 	struct pxa_udc *udc = to_pxa(g);
 
-	stop_activity(udc, driver);
+	stop_activity(udc, NULL);
 	udc_disable(udc);
 	dplus_pullup(udc, 0);